1// Copyright 2014 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#include "components/rappor/rappor_metric.h" 6 7#include "base/logging.h" 8 9namespace rappor { 10 11RapporMetric::RapporMetric(const std::string& metric_name, 12 const RapporParameters& parameters, 13 int32_t cohort_seed) 14 : metric_name_(metric_name), 15 parameters_(parameters), 16 bloom_filter_(parameters.bloom_filter_size_bytes, 17 parameters.bloom_filter_hash_function_count, 18 (cohort_seed % parameters.num_cohorts) * 19 parameters.bloom_filter_hash_function_count) { 20 DCHECK_GE(cohort_seed, 0); 21 DCHECK_LT(cohort_seed, RapporParameters::kMaxCohorts); 22} 23 24RapporMetric::~RapporMetric() {} 25 26void RapporMetric::AddSample(const std::string& str) { 27 bloom_filter_.AddString(str); 28} 29 30ByteVector RapporMetric::GetReport(const std::string& secret) const { 31 // Generate a deterministically random mask of fake data using the 32 // client's secret key + real data as a seed. The inclusion of the secret 33 // in the seed avoids correlations between real and fake data. 34 // The seed isn't a human-readable string. 35 const std::string personalization_string = metric_name_ + 36 std::string(bytes().begin(), bytes().end()); 37 HmacByteVectorGenerator hmac_generator(bytes().size(), secret, 38 personalization_string); 39 const ByteVector fake_mask = 40 hmac_generator.GetWeightedRandomByteVector(parameters().fake_prob); 41 ByteVector fake_bits = 42 hmac_generator.GetWeightedRandomByteVector(parameters().fake_one_prob); 43 44 // Redact most of the real data by replacing it with the fake data, hiding 45 // and limiting the amount of information an individual client reports on. 46 const ByteVector* fake_and_redacted_bits = 47 ByteVectorMerge(fake_mask, bytes(), &fake_bits); 48 49 // Generate biased coin flips for each bit. 50 ByteVectorGenerator coin_generator(bytes().size()); 51 const ByteVector zero_coins = 52 coin_generator.GetWeightedRandomByteVector(parameters().zero_coin_prob); 53 ByteVector one_coins = 54 coin_generator.GetWeightedRandomByteVector(parameters().one_coin_prob); 55 56 // Create a randomized response report on the fake and redacted data, sending 57 // the outcome of flipping a zero coin for the zero bits in that data, and of 58 // flipping a one coin for the one bits in that data, as the final report. 59 return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins); 60} 61 62} // namespace rappor 63